hi,
my 2 cents :
i had to install a libcelt0-0 (apt-get install libcelt0-0) to make it work with my personal server as it is asked in one of the previous msg.

if you run "sudo mumble" you will access to the full gui, could be usefull to set up, but do not know if the setup is saved for the user user (:-))

and it is working good, there is an echo, but the option to reduce echo add a very important delay, so echo cancelation is not usefull .

and : Great, mumble working on N900 this is amazing !!